Precision balance or mass comparator with module for detecting a measurement uncertainty

ABSTRACT

A precision balance including a weighing chamber ( 16 ), a draft shield ( 18, 20, 22 ) which surrounds the weighing chamber, a climate module ( 34 ) which is detachably disposed in the weighing chamber, a processor ( 32 ), a data input unit, and a data transmission path over which data is exchanged between the climate module and the processor. The processor has a measurement uncertainty determining module ( 33 ) with which the measurement uncertainty of the balance is determined. Also disclosed are a method for determining a measurement uncertainty of a balance and a climate module  4  that forms a self-contained modular unit, and includes an air pressure sensor ( 62 ), an air humidity sensor ( 54 ) and an air temperature sensor ( 52 ). A data transmission path transmits data to a processor external to the climate module.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of International Application PCT/EP2014/002853,which has an international filing date of Oct. 22, 2014, and thedisclosure of which is incorporated in its entirety into the presentContinuation by reference. The following disclosure is also based on andclaims the benefit of and priority under 35 U.S.C. §119(a) to GermanPatent Application Nos. DE 10 2013 018 767.2, filed Nov. 8, 2013, and toDE 10 2014 101 563.0, filed Feb. 7, 2014, which are also incorporated intheir respective entireties into the present Continuation by reference.

FIELD OF THE INVENTION

The invention relates to a precision balance or a mass comparator.

BACKGROUND

In high-resolution electronic precision balances and mass comparators ofthis type, the problem presents itself that a plurality of externalparameters influence the result of the weighing. If, during the massdetermination of a test sample or during a weighing procedure, themeasuring error is to be smaller than 10 ppm, the user can hardly avoidconsideration of the measuring uncertainty.

The measuring uncertainty is influenced, inter alia, by the air densityprevailing during the measurement, which affects the buoyancy on thetest sample and is dependent on the ambient temperature, the airpressure and the air humidity. The user also exerts an influence on themeasurement results and thus on the measuring uncertainty, since themanner in which the measurement is carried out influences how exactly aparticular measurement result can be reproduced.

DE 37 14 540 C2 discloses a method for automatic calibration of ahigh-resolution balance in which the balance goes through a sequence oftest steps in which the disturbance variables influencing the weighingresult are compared with limit values and, if the limit values areexceeded, a calibration is carried out.

DE 299 12 867 U1 discloses a balance which has at least one measurementvalue sensor for climate parameters. The measurement values are outputon a separate display unit.

EP 0 864 852 A2 discloses an electronic balance which is calibrated byweighing the same load several times and these data are statisticallyevaluated in order to increase the measuring accuracy.

If the measurement uncertainty of the weighing procedure is to beestimated, all these influencing factors are taken into account. Forthis purpose, guidelines are given in the international recommendationsof OIML R111 as to how the estimation of uncertainty is to be made. PCprograms and Excel-based solutions for uncertainty calculation are knownfrom the background art for this purpose. In the formulae used there,details relating to the balance, the climate and the reference weightsare to be input. In addition to the PC which carries out thecalculation, external sensors with which the climate data are acquiredare also needed. The software in the PC calculates a total uncertaintyfor the weighing process from the weighing results of the balance, theclimate sensor values, the input parameters of the reference weights andthe other uncertainty parameters.

The disadvantage of this solution lies therein that data from aplurality of systems (balance, climate sensors for air densitydetermination, reference weights, etc.) must be transferred to a PC.Herein lies the fundamental risk of a faulty input. Also, a PC whichcarries out the calculation of the uncertainty and accesses a databasewith information (for example, information concerning the referenceweights used) is always required for the evaluation. The computer has noinfluence on the overall weighing process; it can only read weighingresults from the balance. Thus, simplifying, the balance can be regardedas a sensor which supplies the weighing results.

SUMMARY

It is an object of the present invention to provide a precision balanceor a mass comparator and a method with which the determination of themeasurement uncertainty is facilitated and the measurement uncertaintycan be output directly together with the weighing result.

In order to achieve this object, according to one formulation of theinvention, a precision balance is provided, having a weighing chamber, adraft shield which surrounds the weighing chamber, a climate modulewhich contains an air pressure sensor, an air humidity sensor and an airtemperature sensor and is removably arranged in the weighing chamber, aprocessor, a data input unit, and a data transmission path over whichdata can be exchanged between the climate module and the processor,wherein the processor contains a measurement uncertainty determiningmodule with which the measurement uncertainty of the balance can bedetermined. According to further formulation, this object is achievedwith a method for determining the measurement uncertainty of a precisionbalance of this type or of a mass comparator is provided, having aweighing chamber which is separated from the surroundings by a draftshield and in which an air pressure sensor, an air humidity sensor andan air temperature sensor are arranged, wherein the sensors are coupledto a data transmission path and wherein the sample to be weighed isweighed in the form of a test sample. During the weighing process, theair pressure, the air humidity and the air temperature in the weighingchamber are determined s with the sensors. Furthermore, the test sampleis weighed. Then the following uncertainties are determined, forexample, according to OIML R111-1: standard uncertainty of the weighingmethod, uncertainty due to the normal being used, uncertainty of thebalance and the uncertainty of the air buoyancy correction. Finally, atotal uncertainty of the mass determination is ascertained. Theinvention is based on the underlying concept of integrating all thecomponents that are needed for determining the measurement uncertaintyinto the balance. The climate module supplies the data regarding themicroclimate which prevails around the test sample, that is, within thedraft shield. Any changes of the microclimate during the weighingprocess are also immediately incorporated into the determination of themeasurement uncertainty. It is not necessary to input the acquiredclimate data and their uncertainties by hand; erroneous input is thusprevented. Since all the components necessary for determining themeasurement uncertainty are integrated into the balance itself, it canbe transported by the operator in the manner of a self-containedweighing laboratory to where the weighing procedure is to be performed.

Generally expressed, it can be provided that the user is reliably guidedthrough the weighing process, for example, during the measurementcalibration according to OIML R111-1 and that therein, alongside theconventional mass, the real mass and all the relevant uncertainties arealso calculated. At the end of the mass calibration, the balance issuesan evaluation of the test weights according to pre-defined accuracyclasses and all the necessary data are made available for the productionof a test certificate. The balance functions like a mass laboratorysince all the required sensors and data for mass determination areintegrated into the balance.

The balance preferably contains a user interface (display) in order toguide the user, for example, through a mass calibration according to apre-defined sequence program. The load change from reference weights andtest weights necessary for mass determination are recognized and in theevent of an erroneous operation, the mass calibration is terminated. Thebalance makes plausibility tests and evaluations based on the standarddeviation of the mass differences between the reference weight and thetest sample and compares these with earlier standard deviations. Thepermitted uncertainties for an accuracy class of weights to becalibrated are checked and evaluated. The balance can also open thedoors of the draft shield automatically in order to enable a loadchange. All the necessary sensors for mass determination are integratedinto the balance and the uncertainties of all sensors are stored in thebalance in order to calculate a total uncertainty for the massdetermination.

The standard uncertainty of the weighing method uw (type A) isdetermined with an averaged standard deviation sp of the balance (ondifferent days) or alternatively from the standard deviation from massdifferences between the reference weight and the test sample. Theuncertainties (type B) of the reference weights u(mcr) and theinstabilities of the reference weights Uinst(mcr) are stored in thebalance and are used for calculating the total uncertainty. Theuncertainty (type B) of the air buoyancy correction ub is calculatedfrom the uncertainties of the climate sensors for temperature, airpressure and relative humidity integrated into the balance as well asfrom the uncertainties of the densities of reference weights and testweights as well as the uncertainty portion of the formula forcalculating the air buoyancy correction. The uncertainty portions of thebalance uba are calculated from the uncertainty by the displayresolution of the digital balance, the uncertainty due to the off-centerloading, through magnetic influences of the sample (or the weights) andthe uncertainty factor based on the sensitivity of the balance.

To solve the aforementioned problem, a climate module for releasableelectrical coupling to a precision balance or mass comparator is alsoprovided, wherein the climate module forms a self-contained modular unitand has an air pressure sensor, an air humidity sensor and an airtemperature sensor, as well as a part of the data transmission path viawhich the data can be transmitted to a processor outside the climatemodule. Since the climate module is interchangeable (thus, releasablefrom the balance without destruction), if required, it can be sent to anexternal institution or service provider for calibration. In theinterim, the precision balance or the mass comparator can continue to beoperated in that a replacement climate module is used. Thus, one or (inthe case of a plurality of precision balances) a plurality of theclimate modules can be used, in a rolling manner, for calibration whilemeasurements are made with the other climate modules. Overall, a compactweighing laboratory is made available to the user, which can even beconfigured transportable and in which all the components and functions,which are necessary for an air buoyancy correction of weighing results,are to be united in the precision balance or mass comparator. Therefore,no external computers, sensors, etc. are needed. With regard to themeasurement uncertainty, a further advantage is that older balances canbe retrofitted. Aside from the data transmission path, for this purpose,only the software of the processor must be amended.

With regard to accuracy, the precision balance according to theinvention has the advantage that the climate data are measured behindthe draft shield (and not only in the room in which the balance issituated). Therefore, the air density is determined in the immediatevicinity of the test sample. Furthermore, since the buoyancy values andtheir measurement uncertainties are automatically transferred to theprocessor, transmission errors which can occur during the transmissionof values from the “calibration certificate” to a calibration softwarepackage can practically be precluded.

According to one embodiment, it is provided that the climate module isconnected via an electric plug connection or over a wirelesstransmission to the processor. The plug connection can be integratedinto a mechanical receptacle which serves for mounting the climatemodule on the precision balance. In this way, the data transmission pathto the processor is created automatically when the climate module isarranged at its place within the draft shield. On use of a wirelesstransmission, the climate module can be arranged at an arbitrary sitewithin the draft shield, for example at a side wall where it is leastobtrusive, without the need to ensure that a plug connection can bearranged at this site. Furthermore, dispensing with a plug connection isadvantageous in that the interior space of the weighing cabin can beconfigured smoother and therefore more easily cleaned.

It can also be provided that a sensor for determining the degree ofionization in the weighing chamber is present and is linked to the datatransmission path. As a result, an additional parameter can bedetermined and taken into account during the correction of the weighingresult. Depending on the degree of ionization, an output signal isgenerated by the processor, for example, in order actively to change thedegree of ionization in that an ionization device is used which isactivated after reaching a particular degree of ionization. Furthermore,a display can make the user aware that the degree of ionization withinthe weighing chamber is too high and should be discharged.

It can also be provided that a light sensor which is coupled to the datatransmission path is provided in the weighing chamber. As such, anadditional parameter can be determined and taken into account during thecorrection of the weighing result. The processor can emit an outputsignal above a pre-determined incident light level. The influence of theincident light level on the weighing process is therefore determinablein order to take measures, if needed, during the process. The outputsignal can also be a display.

According to one embodiment, it is provided that the processor isconfigured so that, on the basis of the density of the sample to beweighed, it determines the air buoyancy of at least the test sample orthe buoyancy correction factor from the air pressure, the air humidityand the air temperature in the weighing chamber. In this way,metrologically traceable climate values with which the processor is ableto correct the weighing result and to determine and display the mass orthe conventional mass can be obtained and fed back by the climate modulesynchronously with the receipt of the weighing result.

According to one embodiment, an electronic memory is provided, inparticular an EEPROM, which is readable by an external reader and inwhich calibration values and correction values for the climate modulecan be stored. For adjustment, the calibration values and correctionvalues can be stored in an electronic memory on the climate module, inparticular on an EEPROM. This can also take place without a balance.When the climate module is coupled again to the precision balance, thesedata are directly available to the processor of the balance. Inaddition, inter alia at least some of the following information can beplaced in the memory for sensor calibration: the number of thecalibration certificate, the current calibration values, the calibrationdate, the name of the calibrating laboratory and the technician, as wellas the calibration history. “Uncertainty values” for each climatevariable can also be placed in the memory of the climate module so thatfor example, in order to calculate the air density, the calculation ofthe uncertainty of the air density is also performed by the precisionbalance.

According to one embodiment, it is provided that the climate module isalso usable outside a balance as an independent unit and is connectablevia an PC bus to a USB port of a PC. This facilitates the externalcalibration. In addition, the climate module can be used in otherimplementations to record climate variables without being connected to abalance. For this purpose, with little effort, the circuit board of theclimate module can have a plug-in extension so that it can be connectedto a USB adapter.

In order to solve the aforementioned problem, a method for determiningthe measurement uncertainty of a precision balance is further provided,with a weighing chamber which is separated by a draft shield from thesurroundings and in which an air pressure sensor, an air humidity sensorand an air temperature sensor are arranged, wherein the sensors arecoupled to a processor and wherein a sample to be weighed in the form ofa test sample are weighed. Herein, the air pressure, the air humidityand the air temperature in the weighing chamber are determined with thesensors and the test sample is weighed. Furthermore, the standarduncertainty of the weighing method and the uncertainty of the mass ofthe test sample are determined. From this, a total uncertainty of theweighing result is determined. With regard to the resulting advantages,reference is made to the description above.

Furthermore, it can be provided that during the determination of thetotal uncertainty, the result of earlier determinations of the totaluncertainty is also taken into account. Using the total uncertaintydetermined in earlier measurements, firstly, a plausibility estimationof the currently determined total uncertainty can be undertaken. If thepreviously determined total uncertainty was notably lower than thatcurrently determined, an indication can be issued to the user that theoverall weighing procedure has not proceeded satisfactorily. Secondly,the currently determined total uncertainty can be corrected upwardsomewhat if currently a total uncertainty has been determined that isnotably below the total uncertainty of earlier weighing procedures.

Further features and advantages of the invention are disclosed in thefollowing description and the attached drawings, to which reference willbe made. In the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a precision balance according to theinvention,

FIG. 2 is a perspective view of a climate module according to theinvention which can be used with the precision balance according to theinvention,

FIG. 3 is a side view of the climate module of FIG. 2 without the outerhousing,

FIG. 4 is a plan view of the climate module of FIG. 2, also without theouter housing,

FIG. 5 is a flow diagram which illustrates a method for operating thebalance, and

FIG. 6 is a flow diagram which illustrates a method for determining thetotal uncertainty of a mass comparison in accordance with OIML R111-1carried out with the balance.

DETAILED DESCRIPTION

FIG. 1 shows a high-resolution electronic precision balance which inthis exemplary embodiment enables mass comparisons in all the accuracyclasses under OIML R111-1 and also according to ASTM E617-13.

The precision balance comprises a load cell 14 with a base 12. The loadcell 14 also comprises a weighing chamber 16 which is provided by adraft shield with adjustable side walls 18, a front wall 20 and a rearwall 22. The weighing chamber 16 is separated from the surroundings bythe draft shield. A balance dish 24 serves for placement of the sampleto be weighed. These components together form a weighing module 10

An electronic evaluation system 26 configured herein as a separate partis electronically linked via a cable 28 to the load cell 14. A displayunit 30 which is linked to the evaluation system 26 serves both as adisplay and also as a data input unit. While the electronic evaluationsystem 26 and the display 30 are embodied as components physicallyseparated from the weighing module 10 in the illustrated embodiment,other embodiments can incorporate one or both of these components 26 and30 into the weighing module 10.

Among other things, a processor 32 which receives data from the loadcell 14 is accommodated in the electronic evaluation system 26.

Also provided in the electronic evaluation system 26 is a measurementuncertainty determination module 33 with which the measurementuncertainty of a current weighing process can be determined.Furthermore, a memory in which the total uncertainty of earlier weighingprocesses is stored is also integrated into the measurement uncertaintydetermining module 33.

Provided in the weighing chamber 16 is a climate module 34 which isconfigured as a structurally separate unit which can mechanically couplevia a releasable plug connection to the rear wall 22 (that is, it ismounted to be non-destructively releasable), preferably without the aidof a tool.

For this purpose, the rear wall 22 has two slots 36 spaced from oneanother in which flexible locking hooks 38 (see also FIG. 2) lock ontothe outer housing 40 of the climate module.

The climate module 34 is shown in detail in FIGS. 2 and 4.

The outer housing 40 has numerous openings 42 via which the interior ofthe outer housing 40 transitions into the weighing chamber 16 and ispart of the weighing chamber 16 so that the climate in the interior ofthe weighing chamber 16 corresponds to that in the interior of the outerhousing 40.

The climate module 34 is linked electronically via an electric plugconnection to a corresponding plug receptacle 44 in the rear wall 22.The plug receptacle 44 is electrically linked to the processor 32. Aplug 46 with contacts 48 on the climate module 34 is inserted into theplug receptacle 44. Thus the plug 46 forms a module-side part of theelectrical plug connection.

As an alternative to an electric plug connection, a wirelesstransmission, for example, WLAN or Bluetooth, can be used.

The electrical plug connection (or the alternatively used wirelesstransmission) forms a data transmission path with which data can betransferred from the climate module 34 to the processor 32 and possiblyback again.

The plug 46 is preferably a portion of a circuit board 50 on which aplurality of sensors are arranged for detecting the climate in theweighing chamber 16. Thus, an air temperature sensor 52, an air humiditysensor 54, a light sensor 56 arranged in the immediate vicinity of anopening 42 and a sensor 58 for detecting the degree of ionization in theweighing chamber 16 are provided on the circuit board 50, as well as anelectronic memory 60. An air pressure sensor 62 is electrically andmechanically connected via a holder 64 to the circuit board 50.

A plurality of the sensors can also be grouped together into combinedsensors.

A wall 66 closes the shell-like outer housing 40 so that the narrow,tongue-like portion of the circuit board 50 positioned to the right ofthe wall 66 in FIG. 4 is pluggable into the rear wall 22 and into theplug receptacle 44.

Each sensor is linked to the processor 32 through suitable contacts 48.The memory 60 is also linked to the processor 32.

When operated as a comparator balance, the balance functions accordingto the following method, described by reference to FIG. 5:

The density of the sample to be weighed (test weight, also referred toas test sample B, and reference weight A) is input into the comparatorbalance in steps 100 and 102, for example via the display unit 30 whichsimultaneously serves, with a touch screen, as a data input unit.Alternatively, the density of the sample to be weighed can be input inadvance.

A sample to be weighed is placed on the balance dish 24 afterpre-settable process steps, for example, firstly the reference weight A,subsequently the test sample B twice and finally the reference weight Aagain. This involves a comparison weighing (double substitution) fromwhich in step 104, the display difference of the balance is given. Othersequence steps are also possible, for example, ABA rather than ABBA.

The air pressure, the air humidity and the air temperature aredetermined in step 106 via the sensors 62, 54 and 52 and thecorresponding data are then passed on to the processor 32.

The air density is determined in the processor 32 in step 108. Using theinput densities, in the processor the air buoyancy correction factor isdetermined in step 110 and/or the air buoyancy of the sample to beweighed is determined dependent on the air pressure, air humidity, airtemperature and the density of the sample to be weighed and, in step112, the conventional weighing result of the test sample, i.e. the massof the test sample B corrected by its air buoyancy is determined andreproduced as a protocol in the display unit 30, wherein theconventional mass 114 of the reference weight is included in thedetermination of the conventional mass of the test sample.

Furthermore, calibration values and correction values that were storedin the climate module 34 during the calibration of the climate module 34are stored in the memory 60.

This calibration takes place outside the comparator balance. For thispurpose, the climate module 34 is simply unplugged from the weighingchamber 16 without a wire connection needing to be released. The climatemodule 34 is then sent to a suitable calibration center which places thenumber of the calibration certificate, i.e. the new calibration values,the calibration date, the name of the calibrating laboratory andhandling technician and the calibration history, into the memory 60.These values are later read out by the application program when theclimate module 34 is in the precision balance or comparator balanceagain and is used directly in the calculation.

The values of the light sensor 56 and of the sensor 58 for determiningthe degree of ionization in the weighing chamber 16 are also determined.

For example, if the incident light level is raised, a suitable signal isoutput to the display that, for example, the measurement is inaccuratedue to increased exposure to light and therefore an altered temperaturein the weighing chamber. Thus an output signal dependent on the incidentlight level is emitted by the processor.

As soon as the degree of ionization is too high, an ionization devicewhich ionizes the air in the weighing chamber is activated and providesfor discharging of the sample to be weighed, or a warning of excessivecharging of the sample to be weighed is issued.

The memory 60 is preferably an EEPROM.

Furthermore, the connection between the climate module 34 and the restof the precision balance or comparator balance is realized with an PCbus.

The climate module 34 can be connected via a USB adapter into which itis plugged, to a computer in order to calibrate the sensors 52 to 58 and62 without the climate module 34 having to be connected to the weighingmodule 10.

The total uncertainty of the mass determination is determined in thefollowing way (see also FIG. 6):

Firstly, the standard deviation s is determined from the results of thecalibration cycles. This is compared with the averaged standarddeviation sp as found from previous measurements. The standard deviationdetermined for these measurements is stored in a memory of themeasurement uncertainty determining module 33. If the difference betweenthe current standard deviation and the averaged standard deviation ofthe earlier measurements is greater than a value defined as reasonable,the current weighing procedure is terminated. Otherwise, the uncertaintyof the type A weighing process is determined from the standarddeviation.

The type B uncertainty of the air buoyancy correction ub is calculatedfrom the uncertainties of the air density, the material density of thereference and the material density of the test sample. The values forthe uncertainty of the air density are stored in the climate module 34,where they were stored during its calibration.

The type B uncertainty of the balance uba is calculated on the basis ofthe uncertainty due to the sensitivity of the balance uE, theuncertainty due to the display resolution of the balance ud, theuncertainty of the balance due to eccentric loading uE and theuncertainty of the balance due to magnetism uma.

From the values for the type B uncertainty of the air buoyancycorrection and the type B uncertainty of the balance, from the type Auncertainty for the weighing process and additionally from the knownuncertainty of the mass of the reference, the broader total uncertaintyof the weighing process is calculated. The special advantage liestherein that this can be realized integrated within the balance by themeasurement uncertainty determining module 33 to which merelyinformation concerning the test sample and the reference used must beinput. All the other data are either stored therein or are automaticallyrequested, for example, by calling the uncertainty values stored in theclimate module. This enables the relevant total uncertainty to be givenautomatically for a weighing process.

LIST OF REFERENCE NUMERALS AND CHARACTERS

-   10 weighing module-   12 base-   14 load cell-   16 weighing chamber-   18 side wall-   20 front wall-   22 rear wall-   24 balance dish-   26 evaluation system-   28 cable-   30 display unit-   32 processor-   33 measurement uncertainty determining module-   34 climate module-   36 slots-   38 locking hook-   40 outer housing-   42 openings-   44 plug receptacle-   46 plug-   48 contacts-   50 circuit board-   52 air temperature sensor-   54 air humidity sensor-   56 light sensor-   58 sensor-   60 memory-   62 air pressure sensor-   64 holder-   66wall-   100 step-   102 step-   104 step-   106 step-   108 step-   110 step-   112 step-   114 conventional mass of reference weight-   A reference weight-   B test sample

What is claimed is:
 1. Precision balance, comprising: a weighingchamber, a draft shield which surrounds the weighing chamber, a climatemodule which comprises an air pressure sensor, an air humidity sensorand an air temperature sensor, and which is detachably disposed in theweighing chamber and is configured to mount within an to detach from theweighing chamber, a processor, a data input unit, and a datatransmission path over which data is exchanged between the climatemodule and the processor, wherein the processor comprises a measurementuncertainty determining module with which a measurement uncertainty ofthe balance is determined.
 2. The precision balance as claimed in claim1, wherein the data transmission path comprises an electrical plug-inconnection or a wireless transmission path.
 3. The precision balance asclaimed in claim 1, further comprising a sensor coupled to the datatransmission path and configured to determine a degree of ionization inthe weighing chamber.
 4. The precision balance as claimed in claim 1,wherein the weighing chamber comprises a light sensor, which is coupledto the data transmission path.
 5. The precision balance as claimed inclaim 1, wherein the processor is programmed to determine, based on adensity of a substance to be weighed, an air buoyancy of at least a testsample or a buoyancy correction factor from the air pressure, the airhumidity and the air temperature in the weighing chamber.
 6. Theprecision balance as claimed in claim 1, wherein the measurementuncertainty determining module comprises a memory that stores results ofearlier determinations of the measurement uncertainty.
 7. Method fordetermining the measurement uncertainty of a precision balance thatcomprises a weighing chamber, which is separated from a surrounding areaby a draft shield and in which an air pressure sensor, an air humiditysensor and an air temperature sensor are disposed, wherein the sensorsare coupled to a processor and wherein a test sample is weighed, saidmethod comprising: determining the air pressure, the air humidity andthe air temperature in the weighing chamber with the sensors; weighingthe test sample; determining a standard uncertainty of the weighing ofthe test sample; determining a standard uncertainty of the mass of thetest sample; and determining a total uncertainty of the massdetermination.
 8. The method as claimed in claim 7, further comprisingweighing a reference weight in addition to the test sample.
 9. Themethod as claimed in claim 7, wherein the determination of the totaluncertainty comprises factoring in results of earlier determinations ofthe total uncertainty.